This is a feature request similar to my project folder idea:

Enabling users to assign context under other context. Essentially with a nested context folder the user can achieve the benefit of having a very clear top-level context list. This is especially helpful for more powerful users when the number of contexts start to get beyond 20.

- tasks assigned to child context will also be assigned to parent context
- users can browse further to cover all the fine details.

A typical user scenario, where you have a workplace context, and multiple contact person under that context, and maybe a meeting context as well. So all work-related things are assigned to the top-context (workplace), and related topics are assigned only to the specific person (as a child context), or the meeting (another child context).